The Effect Of Branch Bending Angle On Physiological Characteristics And Growth In Apple Tree

‘Fuji’ is the most widely grown apple cultivar in China because of its good quality, longstorage and easy transportation，but has a severe biennial fruiting habit in the Loess PlateauRegion of China even if the interstock ‘M26’ was used. Bending branch has been used toinduce floral buds in ‘Fuji’ apple for a decade in China. The effect of branch bending angle onphysiological characteristics of ‘Fuji and Gala’ apple were studied in order to provide a basisfor the apple industry and for the theoretical research. The main research includes:(1)Proportion of spur (<5cm), medium (5-15cm), long (>15cm) shoots in response to threebending levels of ‘Fuji’ and ‘Gala’ apples;(2) The photosynthetic rate of single leaf in theshoot and whole shoot in response to three bending levels of ‘Fuji’ and ‘Gala’ apples;(3)Nutrient accumulation in the shoot terminals of ‘Fuji’ and ‘Gala’ apples in response tothree different levels of branch bending;(4) Distribution rates of ‘13C’ and ‘15N’ in every partof apple tree through ‘13C’ and ‘15N’ tracking in apple tree in response to three levels ofbranch bending of ‘Fuji’ apples;(5) Dynamic course of Endogenous Hormones of Shootsterminal in Fuji and Gala Apple tree influenced by three different levels of branch bending;(6)Proportion of flower buds of the terminal buds in the shoots in response to three bendinglevels of ‘Fuji’ and ‘Gala’ apples;(7)Average content of sugars, organic acids and phenoliccompounds in ‘Fuji’ apples in response to three levels of branch bending.Number and proportion of the spurs was increased and number of the long and themedium shoots was decreased with increasing bending angles, suggesting that bending with alarger angle can inhibit more vegetative growth of the branches; this is more obvious in ‘Fuji’apple.‘Fuji’ apple was more sensitive to bending levels than ‘Gala’ apple, and a higherproportion of spurs were found on the branches when they were bent at a larger angle in ‘Fuji’apple. There were more acrotony shoots under the lower branch bending level, more basitonyshoots, spurs and spur flower buds with increasing bending levels, and a small number ofterminal flower buds in medium-long shoots in ‘Fuji’ apple. In ‘Gala’ apple, proportion ofterminal flower buds in both spurs and long-medium shoots had no significant variation (P <0.05) between90°and110°. Proportion of terminal flower buds in ‘Gala’ apple was higherthan ‘Fuji’ apple; it showed that ‘Gala’ apple is easier to form terminal flower buds. Thephotosynthetic rate of the single leaf and whole branch were increased with increasing level of branch bending.Total sugar and ratio of C/N in the shoot terminals were increased while total nitrogenconcentration in the shoot terminals decreased with the increasing of bending angles. Totalsugar concentration, total nitrogen concentration and ratio of C/N in the shoot terminalspresented significant variation among three bending levels in both ‘Fuji’ and ‘Gala’ apples.Average of total sugar concentrations in spur apexes was significantly higher than inlong-medium shoot terminals. Thus, branch bending stimulated more carbon accumulation inthe spurs than in the long-medium shoots. Total sugar concentrations and ratio of C/N showedsignificant variation among four sampling dates; and total nitrogen showed significantvariation in most sampling dates in both cultivars.Increase of branches bent angle caused a rise in endogenous ABA and ZR production,and a decrease in the concentration of IAA and GA in shoot terminals. Average of ABA andZR concentrations in spur apexs was significantly higher than in long-medium shoot terminals,but the average of IAA and GA concentrations in spur apexs was lower than in long-mediumshoot terminals. ABA, ZR, IAA and GA concentration in spur apexes showed significantdifference with the increasing of bending angles.‘Fuji’ was more sensitive to bending levelsthan ‘Gala’, and the vegetative growth was reduced in ‘Fuji’ apple with a larger angle branchbending. Thus, a larger angle branch bending can stop spur growth as so as early in ‘Fuji’apple, and might cause it to form a floral-bud. But the spurs in ‘Gala’ apple can be stoppedgrowth and might form floral-buds by branch bending under the90°angle. During the wholegrowing season, the ABA concentration in Gala shoots terminals always were higher thanthose in ‘Fuji’, But the IAA was lower than ‘Fuji’.The ‘13C’ content in the shoot terminals and the carbohydrates in the bent branch wereincreased with the increasing of branch bending angles in ‘Fuji’ apple, so in the whole thetransportion of carbohydrates from the labelled branch to other part of the tree was decreased;the transportion was different, deceased to parts up the labelled branch and roots, increased toparts down the labelled branch above ground, and not change to the same horizontal laterals.Carbohydrates were mainly distribute to the leaves, labelled branches, and then to xylem andphloem of labelled branch, shoots, branches up labelled branch, at last to other organs.Average of the carbohydrates in the spur apex were increased with the increasing of branchbending angles in ‘Fuji’ apple, and showed significant variation, this was in favor of formingflower buds. Carbohydrates were mainly transported to up parts under the small branchbending angles, on the contrary, were mainly transported to down parts under large branchbending angle.The content of15N-urea of the whole tree was decreased with the increasing of branch bending angles in ‘Fuji’ apple; the capacity of the root absorption of15N-urea was being weakat the same time, especially for fine-roots. Branch bending could reduce the absorption andtransport of nitrogen fertilizer capacity of the ‘Fuji’ apple tree, caused the polarity weakens oftree, resulted in decrease in utilization of15N-urea of the tree. The utilization of15N-urea ofnew shoots, spur apexs, long-medium shoots terminals, leaves, main roots, thick roots andfine roots were decreased with the increasing of branch bending angles, this is more obviousfor spur apexs, suggesting that bending with a larger angle can inhibit more vegetative growthof the branches, increase C/N in spur apexs, and was in favor of floral-bud formation.Distribution of15N-urea in xylem and phloem of the trunk, new shoots, long-medium shootsterminals and fine roots were decreased with increasing bending levels, while Distribution of15N-urea in spur apexs and leaves were increased with increasing bending levels.15N-ureaabsorbed by roots were mainly distribute to the leaves, and then to main roots, fine roots andthick roots, next to new shoots, at last to spurs and long-medium shoots.Fructose was the most abundant compound of all those quantified sugars in ‘Fuji’ applefruits, followed by sucrose. Glucose and sorbitol content showed a similar range. Amongorganic acids, malic acid especially is the most abundant compound in ‘Fuji’ apple fruits,followed by Citric acid. Fumaric acid concentration was the lowest among the quantifiedorganic acids; nonetheless, the taste effect of fumaric acid on the flavour of fruits is, despiteits scarcity, stronger than the effect of citric acid. Chlorogenic acid was the major phenoliccompound found in ‘Fuji’ fruits. Syringic acid showed nearly one third the concentration ofchlorogenic acid content in this study. Catechin and Sinapic acid content showed a similarrange. Total sugar, content of simple sugar, total phenolic compounds and average content ofevery kind of phenolic compound in ‘Fuji’ fruits were increased, while total organic acidsconcentration and average content of every kind of organic acid in ‘Fuji’ fruits were decreasedwith the increasing of bending angles, and the quality of apple fruits was improved.